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Dyno tuning technic

Old 07-27-2016, 07:31 PM
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Originally Posted by ICDEDPPL
If EGT`s are too high with a rich mixture I`d say it doesn`t need less fuel but may need more timing to burn the fuel off.
I saw lower egts with more fuel. Pulled 4 jet sizes EGTs went up.
I can't speak to how it affected egt but we did advance it as far as 36. Power peaked at 34. I'll check the old sheets for the egt
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Old 07-27-2016, 07:36 PM
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The best thing about a dyno, is using it whats its for, and thats watching what changes the power numbers. Many times, you will see when richening the mixture, the torque numbers INCREASE. Theres a reason this happens, and it kind of applies to what Icdedppl just said.

The richer fuel mixture, simply takes longer to burn. Why would this make the torque output increase? Because now the peak cylinder pressure inside the cylinder, is happening at a later time, where there is more leverage on the crankshaft. You slowed the burn down with more fuel. When in reality, you may have simply had, too much spark advance in the first place.

There is an area, in which we want peak cylinder pressure to be. Controlling that , is spark timing, and fuel mixture. If you make peak cyl pressure happen too early in the cycle, you lose leverage forcing the piston down the bore. Same goes if you make it happen too late.

This misconception, that spark timing is some sort of adjustable power adder, or power reducer, is just that a misconception. The entire goal, is to fire the plug at the right time. The dyno will tell you alot, about whether you are firing it too early, too late, etc, by watching the torque output, as that is what dyno's measure.

So, lets say, you have a air fuel ratio of 11.5, and you are making, say 600ft lbs at 4500rpm, and you have, 32 degrees of timing there. You then change the timing, to say, 29 degrees at 4500RPM, and do another pull. Now the engine maybe makes, 610ft lbs. What happened was that you simply moved where peak cyl pressure is taking place in the cycle, for the BETTER. The engine is not fighting itself as much now. Lets say, you do another pull, this time with 34 degrees of timing at 4500RPM, and the torque reading is 590FT lbs. What happened? You moved peak cyl pressure to early in the cycle, and the crankshaft lost that leverage.

Now, that example was with 11.5 air fuel ratio. The magical timing advance was 29 degrees. What happens if the air fuel ratio was say, 12.5? The leaner mixture will now burn even faster, and in order to find that sweet spot of peak cylinder pressure to piston position, you may now find that lighting the spark off at 27 degrees, is the magical number for best torque output.

In a marine engine, I would rather have the richer fuel mixture, WITH the extra spark timing, because the extra fuel, does cool things. But it all goes hand in hand. Some people FREAK about igntion timing, under the impression that it creates super high cylinder pressures. While it certainly can if the engine KNOCKS, but aside from that, the cylinders pressures aren't necessarily higher with more timing, they just might be at the wrong "time". Which equates to power loss, both with over advanced, or overly retarded spark timing.

Personally, I think most custom high perf engines, even naturally aspirated, run overly advanced timing in the lower rpm range, and overly retarded timing, in the upper rpm ranges. The problem with a typical old distributor setup, is they are RPM based timing. What the engine wants at 3k rpm cruise for timing, might be 34 degrees. What it wants at 3k rpm wide open acceleration, might be 22 degrees. Hence the modern map sensor. Why is that? Again, its about the max cylinder pressure, relative to the pistons position on the stroke. At light load, the intake charge is not very volitle. its a slow burn. So, you need to fire the plug sooner to get that peak psi at the right spot. At wide open, a very fast burning volitle mixture is entering the cylinder, and that requires the spark to be ignited later, to again, put the peak cyl pressure at the right spot.

Everyone has heard of "boost retard" devices. Boost retard devices, were not invented on the premise to save the engine so much. They were invented, because forced induction setups pack a very fast burning charge into the cylinder, which requires retarded spark timing, and doing so, increases the power output. I personally have pulled out 8,9,10+ degrees on a boosted engine with the daytona box, and saw an INCREASE in torque output. So, what does that tell you? If you are firing the plug 10 degrees to soon relative to what the engine "likes", you are simply putting yourself that much closer to spark knocking it. In this scenerio, Going from 34 degrees at 4000rpm, to 25 degrees at 4000, resulted in a power increase, is really no difference, than say at 6000rpm, going from 34 degrees, to 44 degrees. If someone said "i have 43 degrees in my blown BBC" they would get laughed out of the room. But, that really wouldn't be any worse, than having 34 degrees in an engine at 4000, that wants say 25 degrees.

Guys that dummy down there engines on the dyno, whether its retarding timing, adding tons of fuel, thinking they are doing a "safe" tune, are many times, doing just the opposite of their intention.
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Old 07-27-2016, 08:44 PM
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Originally Posted by ICDEDPPL
If EGT`s are too high with a rich mixture I`d say it doesn`t need less fuel but may need more timing to burn the fuel off.
I saw lower egts with more fuel. Pulled 4 jet sizes EGTs went up.
Well I will tell you first hand it does and can happen however only when way over jetted.
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Old 07-27-2016, 09:04 PM
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Merc Racing dyno; 30 minute pull. 30 seconds at each data point.

http://www.mercuryracing.com/dyno-mighty/
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Old 07-27-2016, 09:44 PM
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Originally Posted by SFOcean
Merc Racing dyno; 30 minute pull. 30 seconds at each data point.

http://www.mercuryracing.com/dyno-mighty/
Oh sure, now I feel better. Killing me here.
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Old 07-27-2016, 10:02 PM
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Originally Posted by SFOcean
Merc Racing dyno; 30 minute pull. 30 seconds at each data point.

http://www.mercuryracing.com/dyno-mighty/
That is pretty friggin AWESOME. Man have things changed since the old 600/800sc days.
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Old 07-27-2016, 10:12 PM
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Originally Posted by SFOcean
Merc Racing dyno; 30 minute pull. 30 seconds at each data point.

http://www.mercuryracing.com/dyno-mighty/
i guess that partially justify,s the cost of the merc 1350 engines.i can,t imagine what it cost to build that caliber of a dyno cell.
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Old 07-27-2016, 10:52 PM
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Originally Posted by MILD THUNDER
That is pretty friggin AWESOME. Man have things changed since the old 600/800sc days.
Ya and then even go back a little further. Unreal... Remember when 70 seemed fast? Lol
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Old 07-27-2016, 10:59 PM
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I know its crazy! I see 73 now lol

Originally Posted by getrdunn
Ya and then even go back a little further. Unreal... Remember when 70 seemed fast? Lol
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